Broadly, the invention relates to a diesel engine having a dual injection system for the engine fuel. More specifically, the engine of this invention is designed to operate on a fuel mixture having one or more chemical compositions. The auto ignition temperature of each composition may be the same or different.
Diesel engines are usually designed to operate on an oil-type fuel, such as diesel fuel oil, which is a petroleum distillate. Some diesel engines, however, are arranged to operate on a mixture of gas and oil, such as natural gas and diesel fuel oil. These engines are usually called natural gas diesels, or dual-fuel diesels, and they can be either two- or four-stroke cycle engines. In the normal operation of the diesel which utilizes an oil-type fuel, atmospheric air is first compressed in the cylinder (combustion chamber) to a pressure of about 500 psi. Compression of the air raises its temperature to about 1000.degree. F. The fuel oil is then injected into the compressed, hot air through a fuel injection nozzle, which atomizes the oil. The atomized oil and air mixture rises to its auto ignition temperature, thus causing the fuel to spontaneously ignite, burn and expand. As the burned gas expands it drives the piston downwardly to initiate the power stroke of the engine.
In the normal operation of a natural gas diesel, a mixture of natural gas and air is drawn into the combustion chamber through the intake valve. In the same manner as the oil-burning engine, the combustible mixture is compressed by the rising piston to raise the temperature of the gaseous fuel. Toward the end of the compression stroke a small amount of diesel fuel oil is injected into the combustion chamber, and the resulting mixture ignites, burns and expands. These diesels normally operate at a lower compression ratio than the oil-burning engines.
In both types of the diesel engines described above, the timing of the engine cycle is directly related to the auto ignition temperature of the fuel. Since the fuel composition is a homogeneous mixture of fuel oil and air, the engine can be adjusted for proper timing, using well known techniques. However, once the engine is properly timed, that is, by adjusting the fuel injection timing, a change in the composition of the fuel oil may require re-timing of the engine. For example, any time that a change in the fuel oil composition results in a significant change in the auto ignition temperature of the composition, the injection timing must be changed to accomodate the new fuel. If the fuel injection timing is not changed to correspond with the change in the auto ignition temperature, the fuel being injected into the combustion chamber will either ignite prematurely, or too late. The overall result is very poor combustion of the fuel and inefficient engine operation.
The diesel engine of this invention is not subject to the fuel ignition problem mentioned above. The present engine is equipped with a novel injection system which permits two fuels, each having the same, or a different auto ignition temperature, to be injected into the combustion chamber separately. In the injection sequence the primary fuel is first pumped into a pre-combustion chamber in the engine cylinder head. The primary fuel thus ignites first and produces a flame front for igniting a secondary fuel composition, which is pumped directly into the combustion chamber.